This invention relates to an electroluminescent panel for use in displaying an image, such as alphanumeric symbols, a static picture, a motion picture, and the like, in an input/output device of a computer, and the like.
As will later be described with reference to a few figures of the accompanying drawing, a conventional electroluminescent panel of the type described comprises a transparent substrate, a transparent or first electrode on the substrate, a second electrode opposite to the first electrode, and an electroluminescent layer between the first and the second electrodes.
With this structure, electroluminescent light is emitted from the electroluminescent layer and can be seen through the transparent substrate when an a.c. voltage is supplied between the first and the second electrodes.
It is mentioned here that the first electrode is nearer to the transparent substrate than the second electrode and will be called a front electrode while the second electrode is farther from the transparent substrate than the first electrode and will be called a back electrode.
In order to improve a contrast and a brightness of an image, the conventional electroluminescent panel comprises a light absorption layer of cadmium telluride (CdTe) between the electroluminescent layer and the back electrode. Practically, the light absorption layer has a high light absorption coefficient and serves to absorb external light which is incident onto the transparent substrate and which is directed towards the back electrode. It is needless to say that internal reflection of the electroluminescent light can also be avoided by the light absorption layer.
The light absorption layer is superposed on a dielectric layer. Superposition of the light absorption layer and the dielectric layer results in an increase of the a.c. voltage necessary for luminescence of the electroluminescent layer. This means that a brightness versus applied voltage characteristic is degraded by a stack of the light absorption layer. The increase of the a.c. voltage is liable to dielectric breakdown of the electroluminescent panel.